Flame retardants and compositions containing them

ABSTRACT

Flame retardants having good stability at the processing temperatures of high melting polymers are described. The flame retardants are halogen-containing bis-imides, for example, those of the formula ##STR1## R being defined in the specification.

This is a division of application Ser. No. 760,664, filed Sept. 18,1968.

BACKGROUND OF THE INVENTION

This invention relates to compositions comprising a flammable materialand a flame retardant. More especially, it relates to compositionscomprising macromolecular flammable materials, for example, polymers.The invention also relates to flame retardants and a process for theirmanufacture.

The problem of the flammability of certain materials has receivedconsiderable attention. One method by which the flammability of certainmaterials, especially macromolecular materials, has been reduced is bythe incorporation therein of halogen-containing compounds, bothinorganic and organic. Inorganic halogen-containing compounds often havedeleterious effects on the properties of the materials, or damage theequipment in which the materials are processed, because of theircorrosive nature, and therefore organic halogen-containing compounds,often in combination with inorganic oxides or non-halogenated salts,have been used most extensively.

While the previously proposed organic halogen-containing compounds havebeen accepted, many disadvantages are still associated with their use.Many previously proposed flame retardants have been more or lessvolatile, leading to loss in flame retardance during use of articlescontaining them, as well as in processing. As macromolecular materialshaving higher use temperatures (and, accordingly, higher processingtemperatures) have been developed, the disadvantages of volatileadditives become more marked. In addition, such higher use andprocessing temperatures have shown up deficiencies in the thermalstability of many of these previously proposed organichalogen-containing flame retardants. Thus, many compounds which havebeen readily incorporated in materials processed at 150° C. have faileddue to volatilization, sublimation or decomposition when incorporatedinto a material which is processed at temperatures in the region of 250°C. to 350° C. Further, some of the commercial materials are adverselyaffected by the radiation making them unsuitable for incorporation intocompositions which are to be irradiation crosslinked.

Some additives may, for example, be sensitive to water even whenincorporated into the material, and when additive-containingcompositions are tested with boiling water, the organic compound isdissolved out or hydrolyzed, resulting at best in impaired flameretardance, and often also in corrosion by the hydrolysis products, forexample, the halogen acids, resulting from contact with water. Suchwater sensitivity also shows when the composition is in prolongedcontact with a humid atmosphere.

SUMMARY OF THE INVENTION

It is an object of this invention to provide flame retarded compositionswhich can be processed at elevated temperatures.

It is a further object of the invention to provide a flame retardanthaving low volatility, good thermal stability and low sensitivity towater.

Other objects of the invention will be apparent from the followingdescription of the invention.

Briefly, the present invention provides a composition comprising aflammable material and a halogen-containing bis-imide. The bis-imidessuitable for use in this invention advantageously contain bromine,chlorine, or both of these halogens; bromine-containing compounds arepreferred. Advantageously, the halogen atoms are bonded to carbon atoms,the carbon atoms preferably being aromatic carbon atoms, for example,members of a benzene ring.

Advantageously, the bis-imide contains at least 4, preferably at least8, halogen atoms, preferably at least 4 bromine atoms, which are, asstated above, advantageously bonded to carbon atoms in an aromatic ring.Advantageously, the halogen atoms represent at least about 25% by weightof the molecule.

It will be apparent to those skilled in the art that no precise valuesfor the proportion of the bis-imides in the composition can be given,since this proportion will vary with the particular flammable material,the presence of other additives, the particular bis-imide, and thedegree of flame retardance sought in any given application. Further, theproportion necessary to achieve a given extent of flame retardance in aparticular composition will depend on the shape of article into whichthe composition is to be made, for example, electrical insulation,tubing and film will each behave differently. In general, however, thecomposition may contain from about 5% to about 40%, preferably 20% to30%, of a bis-imide of the present invention, when the bis-imide is theonly flame retardant compound in the composition.

It will be appreciated that one or more bis-imides may be incorporatedin the same composition and that other flame retardant materials may beused in conjunction with the bis-imides. It is especially advantageousto use the bis-imide and a compound, especially the oxide, of a Group Velement, for example, bismuth, arsenic, phosphorus and especiallyantimony, in a composition. Of these compounds, antimony oxide isespecially preferred. If such a compound is present in a composition,the quantity of bis-imide needed to achieve a given flame-retardance isaccordingly reduced.

Accordingly, the present invention also provides a flame retardantsystem comprising a bis-imide in admixture with a compound of a Group Velement, and compositions comprising a flammable material and such aflame-retardant system. The proportions of the bis-imide and thecompound are not critical, but in general the bis-imide and the compoundare conveniently in a ratio of from about 1:5 to about 15:1, preferably1:1 to 9:1.

The compositions may contain up to about 40% by weight of the system,preferably between 20% and 30% by weight. It is believed that theinorganic compound and the halogen-containing bis-imide will react underthe conditions of combustion of a flammable material to form inorganichalogen compounds, e.g., halides and oxyhalides, which assist inretarding combustion. To the extent that the two components of thesystem interact, they should be present in approxmately equivalentproportions. The halogen-bearing component also acts as a flameretardant independently and the proportions in a flame retardant systemare a matter of choice, depending, inter alia, on the material in whichthe system is to be incorporated, and commercial considerations. Thus, amixture in which one component predominates may be regarded as a mixtureof equivalent quantities of the two components blended with the one inexcess.

The flame retardant bis-imides and systems containing bis-imides may beused in combination with virtually any flammable material. The materialmay be macromolecular, for example, a cellulosic material or a polymer.Among polymers with which the bis-imide may be combined there may bementioned, by way of illustrative examples, olefin polymers, forexample, homopolymers of ethylene, propylene, butene, copolymers of twoor more such monomers and copolymers of one or more such monomers withother copolymerizable monomers, for example, ethylene/propylenecopolymers, ethylene/ethyl acrylate copolymers and ethylene/vinylacetate copolymers; polymers of olefinically unsaturated monomers, forexample, polystyrene and styrene copolymers; polyurethanes; polyamides;polyimides; acrylic resins, polyesters, epoxy resins; alkyds; phenolics;elastomers, for example, butadiene/styrene copolymers,butadiene/acrylonitrile copolymers and terpolymers of acrylonitrile,butadiene and styrene; natural rubber; butyl rubber; and polysiloxanes.The composition may contain any of the additives usually present andwhere appropriate to the particular polymers, may be crosslinked bychemical means or by irradiation.

The bis-imides of the present invention advantageously have one of thefollowing general formulae ##STR2## wherein R₁, R₂ and R₃, which may bethe same or different, each represent a divalent organic radical, R₄ andR₆, which may be the same or different, each represent a monovalentorganic radical, R₅ represents a tetravalent organic radical and R₇represents a trivalent organic radical, and wherein R₁, R₂ and R₃ inFormula I, R₄, R₅ and R₆ in Formula II, and R₁, R₇ and R₄ in Formula IIItaken together contain at least one halogen atom, preferably at least 4halogen atoms, advantageously chlorine or bromine atoms, preferablybromine. Advantageously, the halogen atoms represent at least 25% byweight of the molecule and preferably, the halogen atoms are bound toaromatic carbon atoms.

For synthetic reasons, bis-imides of Formulas I and II are preferred,especially Formula I, as are bis-imides in which (in Formula I) R₁ andR₃ are identical, and (in Formula II) R₄ and R₆ are identical; it is tobe understood, however, that the flame retardant effect of thebis-imides is in no way dependent on their being identical. Furthermore,mixtures of one or more compounds of one or more of each of the aboveformulae may be employed.

Subject to the requirement that the bis-imides be halogen-containing,radicals R₁ to R₇ preferably represent radicals such that R₁ (COOH)₂ andR₃ (COOH)₂ are each one of the following:

tetrabromophthalic acid

tetrachlorophthalic acid

1,4,5,6,7,7-hexachlorobicyclo-(2.2.1)-5-heptene-2,3-dicarboxylic acid(chlorendic acid)

5,6,7,8,9,9-hexachloro-1,2,3,4,4a,5,8,8a-octahydro-5,8-methanonaphthalene-2,3-dicarboxylic acid

5,6,7,8,9,9hexabromo-1,2,3,4,4a,5,8,8a-octahydro-5,8-methanonaphthalene-2,3-dicarboxylic acid

phthalic acid

succinic acid

dichloromaleic acid

R₂ (NH₂)₂ is one of the following:

ethylenediamine

1,6hexamethylenediamine

4,4'-methylenedianiline

4,4'-oxydianiline

phenylenediamines

xylylenediamines

tetrachloroxylylenediamines

tetrabromoxylylenediamines

R₄ NH₂ and R₆ NH₂ are one of the following:

2,4,6-trichloroaniline

2,4,6-tribromoaniline

2,3,4,5,6-pentabromobenzylamine

2,3,4,5,6-pentachlorobenzylamine

R₅ (COOH)₄ is one of the following:

pyromellitic acid

naphthalene-1,4,5,8-tetracarboxylic acid

R₇ (NH₂)(COOH)₂ is one of the following:

3- or 4-aminophthalic acid

or imide-forming isomers or substitution products of any of the aboveamines or acids. Further diamines and the dianhydrides of furthertetracarboxylic acids are those listed in U.S. Pat. No. 3,179,632, thedisclosure of which is incorporated herein by reference.

Thus, the compounds mentioned above may be substituted, or furthersubstituted, by halogen atoms, especially by chlorine or bromine atoms,provided that imides may still be formed therefrom. The compounds mayalso be substituted by other groups, for example, alkyl, aryl, alkarylor aralkyl radicals, functional groups and hetero atoms provided thatthe flame retardant properties of the resulting bis-imides are notadversely affected thereby. It will be appreciated that where watersensitivity is undesirable the bis-imide will not contain groups whichwould tend to make the bis-imide more water-soluble. It will also beappreciated that the presence of a substituent group on the radical willnot in general affect the flame retardant properties except to theextent that the molecular weight is increased. Such an increase inmolecular weight would in general mean that a greater weight ofbis-imide is necessary to achieve a given degree of flame retardance ina composition; on the other hand, the change in melting point andvolatility resulting from the presence of, for example, an additionalmethyl or ethyl group in the molecule may well be desirable and offsetthe increase in molecular weight and decrease in proportion of halogenin the molecule.

As illustrative examples of suitable bis-imides, there may be mentioned

N,N'-(p and m-phenylene)-bis[3,4,5,6-tetrachlorophthalimide]

N,N'-(p and m-phenylene)-bis[3,4,5,6-tetrabromophthalimide]

N,N'-(methylene-di-p-phenylene)-bis-[3,4,5,6-tetrachlorophthalimide]

N,N'-(methylene-di-p-phenylene)-bis[3,4,5,6-tetrabromophthalimide]

N,N'-(oxy-di-p-phenylene)-bis[3,4,5,6-tetrachlorophthalimide]

N,N'-(oxy-di-p-phenylene)-bis[3,4,5,6-tetrabromophthalimide]

N,N'-(p and m-phenylene)-bischlorendimide

*N,N'-(p and m-tetrachloroxylylene)-bis[3,4,5,6-tetrachlorophthalimide]

*N,N'-(p and m-tetrachloroxylylene)-bis[3,4,5,6-tetrabromophthalimide]

*N,N'-(p and m-tetrachloroxylylene)-bischloroendimide

N,N'-(1,2-ethylene)-bischloroendimide

N,N'-(1,2-ethylene)-bis[3,4,5,6-tetrabromophthalimide]

N,N'-bis(1,2,3,4,5-pentabromobenzyl)-pyromellitimide

N,N'-bis(2,4,6-tribromophenyl)pyromellitimide

Certain of these compounds are novel and the present inventionaccordingly also provides halogen-containing bis-imides (other thanthose formed from tetrachlorophthalic anhydride andp,p'-diaminodiphenylmethane and 2,4-diaminotoluene), especiallycompounds of the formula ##STR3## in which R represents a divalentaliphatic, aromatic or araliphatic radical which may be substituted byone or more halogen atoms or interrupted by hetero atoms. Preferably R,when it is an aliphatic radical, is an alkylene radical and preferablyit contains from 1 to 18 carbon atoms, especially from 2 to 10 carbonatoms. When R is an aromatic radical, it may contain 1, 2 or more ringsystems which may be joined, when there are two or more, by aliphaticradicals, by hetero atoms, especially oxygen, or directly; the imidenitrogen atoms may be bonded directly to the aromatic system or by analkylene chain. The aromatic rings may advantageously be substituted byone or more halogen atoms, preferably by bromine and especially bychlorine atoms.

More especially, the present invention provides compounds of the FormulaIV in which R represents a radical of the formula ##STR4## in which eachR₈, which may be the same or different, represents hydrogen, an alkylradical containing from 1 to 4 carbon atoms, or a halogen atom, R₉represents an alkylene radical, preferably containing 1 carbon atom, orhetero atom or group, preferably oxygen, or is absent, R₁₀ represents analkylene radical having from 1 to 4 carbon atoms or is absent, and R₁₁represents an alkylene radical having from 1 to 18, preferably 2 to 10,carbon atoms.

The bis-imides may be made by any of the methods in general use ordescribed in the literature for the manufacture of imides. In general,the imide results from heating together the corresponding anhydride andamine with elimination of water, the reactants being dissolved in acommon solvent. Suitable solvents include, for example,N-methyl-2-pyrrolidone, dimethylacetamide, xylene and cresol.

Generally, the imide will be precipitated from the solution eitherduring the reaction or on cooling after reaction. If the imide isrequired pure, the precipitate may be filtered, washed, andrecrystallized from a suitable solvent.

The bis-imides may be incorporated with the flammable material by any ofthe methods normally employed for the admixture of additives to thematerial. For example, when the flammable material is a polymer, thebis-imides, which are solid at room temperature and may generally beobtained in the form of powders, may be blended with granules, pellets,chips or a powder of the polymer in a tumbler or milled into acomposition of the polymer and additives.

The invention will now be illustrated in the following examples, inwhich all parts are by weight unless otherwise indicated.

EXAMPLE 1 Preparation ofN,N'-(2,4,5,6-tetrachloro-m-xylylene)-bischlorendimide

A 1 liter flask was equipped with a nitrogen purge, a heating mantle, amechanical stirrer, a reflux condenser and a Dean-Stark apparatus (agraduated vessel which allows the volume of water in the condensate tobe measured). To 81.6 gms (0.22 mole) of1,4,5,6,7,7-hexachlorobicyclo-(2.2.1)-5-heptene-2,3-dicarboxylicanhydride (chlorendic anhydride) was added 27.4 gms (0.1 mole) of2,4,5,6-tetrachloro-m-xylylenediamine in 500 ml. xylene. The mixture wasrefluxed (at about 140° C.) for 2 hours, after which the reactionmixture was a clear solution, 3.2 ml. of water having been collected inthe Dean-Stark apparatus. The solvent was then boiled off, precipitationoccurring when about 450 ml. of xylene had been removed. The remainingslurry was cooled and filtered to yield fine white crystals which werewashed with methanol. Addition of methanol to the filtrate yielded asecond crystalline precipitate; the infrared (IR) spectra of the twocompounds were identical. The first compound (62.1 gms) had a meltingpoint of 293°-206° C., the second compound (6.9 gms) melted at 285°-290°C., indicating a lower purity. The IR spectrum was indicative of animide and showed no amide absorption. The total yield was 68%.

    ______________________________________                                        Analysis: C.sub.26 H.sub.8 Cl.sub.16 N.sub.2 O.sub.4                                        Calc. %                                                                              Found %                                                  ______________________________________                                        Carbon          31.9     31.8                                                 Hydrogen         0.8      1.3                                                 Nitrogen         2.9      3.0                                                 Chlorine        57.9     58.3                                                 ______________________________________                                    

EXAMPLE 2 Preparation ofN,N'-(p-phenylene)-bis[3,4,5,6-tetrachlorophthalimide]

In a 5 liter round-bottom flask equipped with a heating mantle, astirrer, a thermometer, a condenser and a nitrogen purge, there werereacted 457.5 gms (1.6 mole) of tetrachlorophthalic anhydride and 86.5gms (0.8 mole) of p-phenylenediamine in 2000 ml. ofN-methyl-2-pyrrolidone (NMP), the reactants going into solution as themixture was heated with stirring. At 170° C., precipitation began andcontinued as the temperature was raised to 200° C. where it wasmaintained for 90 minutes. The reaction mixture was then allowed to coolovernight. The cooled mixture was filtered and the yellow precipitatewas recovered. The precipitate was washed with NMP, thoroughly stirredin acetone, filtered and washed with more acetone. The product was driedunder vacuum at 150° C. for 16 hours. 272.7 gms (yield=53%) of anivory-yellow material was obtained, having a melting point in excess of500° C., with some sublimation at about 425° C. The IR spectrum had thecharacteristics of an imide with the absorption bands at 1710s and 1770wcm⁻¹. The product was insoluble in water.

    ______________________________________                                        Analysis: C.sub.22 H.sub.4 Cl.sub.8 N.sub.2 O.sub.4                                         Calc. %                                                                              Found %                                                  ______________________________________                                        Carbon          41.0     41.5                                                 Hydrogen         0.6      0.7                                                 Nitrogen         4.4      4.5                                                 Chlorine        44.0     44.7                                                 ______________________________________                                    

EXAMPLE 3 Preparation ofN,N'-(p-phenylene)-bis[3,4,5,6-tetrabromophthalimide]

108 gms (1.0 mole) of p-phenylenediamine was dissolved in 1 liter ofwarm NMP under a nitrogen atmosphere and the solution filtered to removesuspended particles. This filtered solution was then added to asimilarly prepared filtered solution of 928 gms (2.0 moles) oftetrabromophthalic anhydride in 2 liters of warm NMP in the apparatusdescribed in Example 2. A mildly exothermic reaction took place and themixture was further heated while stirring. At about 145° C.,precipitation began. The quantity of brown precipitate increased withcontinued heating and a further 2 liters of NMP was added to facilitatestirring, the temperature being raised to 200° C. and maintained for 2hours, before the mixture was allowed to cool. The precipitate wascollected, washed with NMP, roughly dried and washed with acetone. Thematerial was then stirred well with acetone, filtered and again washedbefore being dried overnight at 150° C. under vacuum. The product was afine, rusty-gold precipitate with a melting point above 500° C. Theyield was 486 gms (49%), the infrared spectrum having the characteristicimide structure, absorption bands at 1712s and 1765w cm⁻¹. The compoundwas insoluble in water, methanol, ether, xylene, dimethyl sulphoxide anddimethyl acetamide.

    ______________________________________                                        Analysis: C.sub.22 H.sub.4 Br.sub.8 N.sub.2 O.sub.4                                         Calc. %                                                                              Found %                                                  ______________________________________                                        Carbon          26.4     26.7                                                 Hydrogen         0.4      0.5                                                 Nitrogen         2.8      2.9                                                 Bromine         64.0     63.2                                                 ______________________________________                                    

The nonvolatility of the product was demonstrated by subjecting theproduct to a vacuum (1×10⁻⁶ torr.) at a temperature of 300° C. andanalyzing the gas in contact with the product by mass spectrography. Notrace of the product in the gas was found.

EXAMPLES 4 TO 22

The following compounds were prepared under conditions generally similarto those of Example 1, 2 or 3.

                                      TABLE 1                                     __________________________________________________________________________    Ex.           Time                                                                             Temp.    Product Yield                                                                             Mp                                      No.                                                                              Bis-Imide From:                                                                          Hrs.                                                                             °C.                                                                        Solvent                                                                            Character                                                                             %   °C.                              __________________________________________________________________________     4 Chlorendic anhydride                                                                     1  120 Xylene                                                                             Fine white                                                                            85  342-45                                     and MPD                crystals                                             5 Chlorendic anhydride                                                                     1.5                                                                              140 Xylene                                                                             Lavender                                                                              71  >475                                       and PPD                precipitate                                          6 Chlorendic anhydride                                                                     0.5                                                                              140 Xylene                                                                             White   88  328-30                                     and PXD                precipitate                                          7 Chlorendic anhydride                                                                     0.5                                                                              125 Xylene                                                                             White   68  354-56                                     and ND                 crystals                                             8 Tetrachlorophthalic                                                                      0.5                                                                              140 Xylene                                                                             Yellow  95   405                                       anhydride and MPD      precipitate                                          9 Tetrachlorophthalic                                                                      1.0                                                                              195 NMP  Yellow  33  400-10                                     anhydride and MXD      precipitate                                         10 Tetrachlorophthalic                                                                      2.5                                                                              200 NMP  Yellow  19  465 dec                                    anhydride and PXD      precipitate                                         11 Tetrabromophthalic                                                                       2.5                                                                              200 NMP  Fluffy yellow                                                                         44  454-58                                     anhydride and MPD      precipitate                                         12 Tetrabromophthalic                                                                       0.5                                                                              175 NMP  Ivory   57   445                                       anhydride and MXD      precipitate                                         13 Tetrabromophthalic                                                                       2.5                                                                              200 NMP  Yellow ivory                                                                          18  436-40                                     anhydride and PXD      precipitate                                         14 Tetrabromophthalic                                                                       2.5                                                                              200 NMP  Yellow  57  390-95                                     anhydride and MD       precipitate                                         15 Tetrabromophthalic                                                                       2.5                                                                              200 NMP  Yellow  29  410-15                                     anhydride and OD       precipitate                                         16 Tetrabromophthalic                                                                       0.5                                                                              200 NMP  Yellow  26  465 dec                                    anhydride and ED       precipitate                                         17 Tetrachlorophthalic                                                                      0.5                                                                              175 NMP  Light yellow                                                                          58  367-70                                     anhydride and MD       precipitate                                         18 Tetrachlorophthalic                                                                      0.5                                                                              160 DMA  Yellowish                                                                             44  380-83                                     anhydride and OD       precipitate                                         19 Phthalic anhydride                                                                       1.0                                                                              180 NMP  Fine white                                                                            86  285-87                                     and MXD                crystals                                            20 Chloran and PPD                                                                          0.5                                                                              135 Xylene                                                                             Lavender                                                                              45  400 dec                                                           precipitate                                         21 Chloran and PXD                                                                          1.0                                                                              180 NMP  Off-white                                                                             83  410 dec                                                           powder                                              22 Pyromellitic                                                                             17.0                                                                             200 NMP  White powder                                                                          91  >500                                       dianhydride and                                                               pentabromobenzyl-                                                             amine                                                                      __________________________________________________________________________

Where:

ED represents ethylenediamine

MD represents 4,4'-methylenedianiline

OD represents 4,4'-oxydianiline

MPD represents m-phenylenediamine

PPD represents p-phenylenediamine

MXD represents 2,4,5,6-tetrachloro-m-xylylenediamine

PXD represents 2,3,5,6-tetrachloro-p-xylylenediamine

NMP represents N-methyl-2-pyrrolidone

DMA represents N,N'-dimethylacetamide

Chloran represents2,3-dicarboxy-5,8-endomethylene-5,6,7,8,9,9-hexachloro-1,2,3,4,4a,5,8,8a-octahydronaphthaleneanhydride

EXAMPLE 23 Preparation ofp-(3,4,5,6-tetrabromophthalimide)-p'-(3,4,5,6-tetrachlorophthalimide)-diphenylmethane

A heated solution of 13.24 gms (0.046 mole) of3,4,5,6-tetrachlorophthalic anhydride in 25 ml. xylene was added to aheated solution of (26 gms, 0.041 mole)p-amino-p'-(3,4,5,6-tetrabromophthalimide)-diphenylmethane in 425 ml.xylene and the mixture refluxed for 4.5 hours. A yellow precipitate wasfiltered from the hot reaction mixture, washed in turn with hot xyleneand methanol and dried under vacuum at 100° C. The yield was 7.7 gms(21%). After two recrystallizations from dimethylacetamide and methanol,the melting point was 383° C., with decomposition.

The p-amino-p'-(3,4,5,6-tetrabromophthalimide)diphenylmethane wasprepared as follows: 148.5 gms (0.25 mole) of 4,4'-methylenedianilinewas dissolved in 400 ml. of hot xylene, 115.7 gms (0.25 mole) of3,4,5,6-tetrabromophthalic anhydride was dissolved in a second sample ofhot xylene and the two solutions mixed, stirred under reflux for 2hours, and allowed to stand overnight. The mixture was then reheated toboiling, the remaining solid filtered, washed with xylene and methanol,and dried at 100° C. under vacuum. Recrystallization from xylene gavedark orange crystals. On heating the solid, it darkens at 240° C.,decomposition appearing complete at 340° C. Infrared analysis showsbands corresponding to NH₂ (3450 and 1628 cm⁻¹) and imide (1720 and 1765cm⁻¹) groups.

EXAMPLE 24 Preparation ofN,N'-(2,3,5,6-tetrachloro-p-xylylene)-bisphthalimide

In a 3 liter, round-bottom flask equipped with a heating mantle,mechanical stirrer, thermometer, nitrogen inlet and condenser, 137 gms(0.5 mole) of 2,3,5,6-tetrachloro-p-xylylenediamine was dissolved atroom temperature in 1 liter N-methyl-2-pyrrolidone (NMP). Whilestirring, 150 gms (1.0 mole) solid phthalic anhydride was added, thetemperature rising to 47° C. The resulting greenish solution was heatedto 180°-185° C. for 30 minutes, after which period crystallization tookplace. The hot mixture was poured into a 2 liter beaker when masscrystallization occurred.

After cooling to room temperature, the tan crystalline mass wasfiltered, washed with NMP, slurried with acetone and refiltered. Afterpartial air drying, the crystals were dried in a vacuum oven for 2.5hours at 110° C. Yield was 227.9 gms (85%), melting point, 328°-330° C.

    ______________________________________                                        Analysis: C.sub.24 H.sub.12 Cl.sub.4 N.sub.2 O.sub.4                                        Calc. %                                                                              Found %                                                  ______________________________________                                        Carbon          53.88    54.64                                                Hydrogen         2.41     2.30                                                Nitrogen         5.24     5.41                                                Chlorine        26.51    26.51                                                ______________________________________                                    

In the following examples, the symbols have the following meanings:

A=perchloropentacyclo[5.2.1.0²,6.0³,9.0⁵,8 ]decane

B=1,4,7,10-dimethanocycloocta-1,2,3,4,7,8,9,10,13,13,14,14-dodecachloro-1,4,4a,5,6,6a,7,10,10a,11,12,12a-dodecahydro[1,2,5,6]dibenzene

Example 1, etc.=product of Example No. 1, etc.

EXAMPLE 25

Compounds of the invention were blended with poly(1,12-dodecamethylenepyromellitimide) and produced as described in a copending applicationfiled on even date with this application by Edward C. Stivers entitled"Polymers, Process and Articles", the disclosure of which isincorporated herein by reference. This is a high-melting polymer whichis processed at temperatures in excess of 300° C., a temperature atwhich many flame retardants decompose. Compositions containing thepolymer, 2% Irganox 1010 (an anti-oxidant-pentaerythritoltetra-3,5-ditert.butyl-4-hydroxydihydrocinnamate) and a compound of theinvention were pressed into slabs of dimensions 4.0"×0.25"×0.05" at 330°C. and tested according to ASTM D635-63, but modified to test 4 stripsof each composition having the given dimensions. This test, in which aBunsen flame is contacted with one end of the strip, is used to comparethe flammability of different materials. A short time toself-extinction, or a small extent or rate of burning, indicates goodflame retardant properties.

                  TABLE II                                                        ______________________________________                                                 Additive Sb.sub.2 O.sub.3                                                                       Aver. Sec. to                                      Additive PHR      PHR      Self-Extinction                                                                          Dripping                                ______________________________________                                        0         0        0       Burnt      Yes                                     Example 2                                                                              20       10       5          No                                      Example 2                                                                              30       15       0          No                                      Example 3                                                                              25        0       1          No                                      Example 22                                                                             25        0       2          No                                      Example 24                                                                             30       16       2          No                                      ______________________________________                                    

A similar slab containing 20 PHR of compound B was also prepared. Thisslab was black, indicating considerable decomposition of the commercialflame retardant.

EXAMPLE 26

Various compositions of low density polyethylene containing no flameretardant, commercially available flame retardants and the flameretardants of the present invention were prepared. The flammability ofslabs 0.060" thick prepared from the compositions was measured accordingto ASTM D635-63, but modified to test 4 samples of each composition.

                  TABLE III                                                       ______________________________________                                                            Average Burning                                           Run             Additive  Sb.sub.2 O.sub.3                                                                    Extent Rate                                   No.   Additive  PHR       PHR   (in.)  (in./min.)                             ______________________________________                                        1     0          0         0    3.00   1.24                                   2     A         10        20    2.65   1.06                                   3     A         20        10    3.00   0.84                                   4     B         10        20    2.45   0.93                                   5     B         15        15    1.32   0.75                                   6     B         20        10    0.25   0.55                                   7     B         30         0    3.00   0.89                                   8     Ex. 1     10        20    2.00   0.72                                   9     Ex. 1     20        10    0.45   0.53                                   10    Ex. 3     15        15    0.90   0.84                                   11    Ex. 3     20        10    0.25   0.36                                   12    Ex. 3     25         5    0.05   0.27                                   13    Ex. 3     27         3    0.40   0.32                                   14    Ex. 3     28         2    0.50   0.49                                   15    Ex. 3     30         0    0.98   0.47                                   16     Ex. 16   20        10    0.10    0.55*                                 17    Ex. 3     20        10    0.30    0.47*                                 ______________________________________                                         *These samples contained 0.3 parts per hundred resin of Santonox R            [4,4thiobis(6-tert-butyl-m-cresol)].                                     

The reduction in both the rate and extent of burning compared withcompositions containing no flame retardant and commercially availableflame retardants can be seen. There was no dripping from any samplecontaining a flame retardant.

EXAMPLE 27

The following compositions were prepared and formed into slabs 0.060"thick.

    ______________________________________                                                           Parts by Weight                                            ______________________________________                                        Polyethylene (low density DFD                                                                      100                                                      6040)                                                                         2-hydroxy 4-n-octoxybenzophenone                                                                   0.1                                                      (Cyosorb UV 531 light absorber)                                               4,4'-thiobis(6-tert-butyl-m-cresol)                                                                0.1                                                      (Santonox R)                                                                  Flame retardant      See Table IV                                             ______________________________________                                    

50% of the slabs were irradiated to a dose of 15 Mrad from each side.All slabs were tested as in Example 26.

                  TABLE IV                                                        ______________________________________                                                            Average Burning                                           Run              Additive Sb.sub.2 O.sub.3                                                                    Extent Rate                                   No.   Additive   PHR      PHR   (in.)  (in./min.)                             ______________________________________                                              Unirradiated                                                            1     0           0        0    3.00    1.54**                                2     B          20       10    0.75   0.43                                   3     B          30        0    3.00   1.02                                   4     Ex. 3      20       10    0.38   0.66                                   5     Ex. 3      30        0    0.32   0.62                                         Irradiated                                                              6     0           0        0    3.00    1.89**                                7     B          20       10    2.40   0.63                                   8     B          30        0    3.00    1.14*                                 9     Ex. 3      20       10    0.82   0.41                                   10    Ex. 3      30        0    0.38    0.76*                                 ______________________________________                                         **In these tests, dripping of melted material took place.                     *In these tests, there was slight dripping of melted material.           

Table IV shows the superiority of the flame retardant of the presentinvention, especially in the irradiated polyethylene. It will be notedalso that the flame retardant of the present invention is effective inreducing the rate and extent of burning in the absence of any antimonyoxide or similar additive.

EXAMPLE 28

The product of Example 14 was incorporaed into anacrylonitrile-butadiene-styrene polymer (CYCLOLAC X-27, made by MarbonChemical, Division of Borg-Warner Corporation), and slabs of dimensions5.0"×0.5"×0.06" were tested according to ASTM D635-63, modified to testfour samples.

                  TABLE V                                                         ______________________________________                                                  Additive Sb.sub.2 O.sub.3                                           Additive  PHR      PHR        Results                                         ______________________________________                                        0          0       0          Burnt at 2.3"/min.                              Ex. 14    25       12.5       Non-burning;                                                                  3-5 sec. afterglow                              ______________________________________                                    

EXAMPLE 29

Two compounds of the invention were incorporated into polypropylene(Shell W550, a polymer stated to be especially suitable for articleswhich will be exposed to elevated temperatures), the composition waspressed into slabs 5.0"×0.5"×0.06", and tested according to ASTMD635-63.

                  TABLE VI                                                        ______________________________________                                                       Average Burning                                                        Additive Sb.sub.2 O.sub.3                                                                      Extent Rate                                          Additive                                                                              PHR      PHR     (in.)  (in./min.)                                                                           Dripping                               ______________________________________                                        0       0        0              1.2    Yes                                    Ex. 14  26.7     13.3    0.3           No                                     Ex. 1   20       10      0.8           Slight                                 ______________________________________                                    

In general, those compounds of the present invention containing bromineatoms bound to aromatic carbon atoms have higher flame retardance andlower thermal stability than a corresponding compound containingchlorine atoms. It is also believed that in general the thermalstability of a compound containing a halogen atom bound to an aliphaticcarbon atom is lower than that of a similar compound containing the samehalogen atom bound to an aromatic carbon atom. These differences enablethe user to choose a compound of the invention suitable for a particularpurpose. The compounds of this invention can be processed attemperatures which will cause the decomposition of many commerciallyavailable materials.

It is believed that the stability of the compounds of this invention atprocessing temperatures of polymer materials is in part due to theirbeing solid at these temperatures, and accordingly those compoundshaving melting points in excess of about 275° C. are preferred.

It is to be understood that all halogen-containing bis-imides are thesubject of this invention, and that the foregoing examples are intendedto be by way of illustration only and that the compounds of theinvention can be used to flame retard a variety of materials other thanthe polymers hereinbefore described, these compositions indicating onlysome exemplary compositions in which the bis-imides have been foundespecially effective. It is also clearly to be understood that mixturesof two or more bis-imides may be employed when practicing thisinvention. The bis-imides can be combined with the materials commonlyused or proposed for use as flame retardant synergists without departingfrom the ambit of the invention. Thus, the invention is to be regardedas limited only by the lawful scope of the appended claims.

I claim:
 1. A bisimide compound of the formula ##STR5## wherein each Xis independently bromine or hydrogen with the proviso that at least 4 ofsaid X's are bromine, and R represents an alkylene radical of 2 to 18carbon atoms.
 2. A bisimide as claimed in claim 1 in which each said Xis bromine.
 3. A bisimide as claimed in claim 2 in which R is analkylene radical of 2 to 6 carbon atoms.
 4. A bisimide as claimed inclaim 3 which is N,N'-(1,2-ethylene)-bis[3,4,5,6-tetrabromophthalimide].5. A bisimide as claimed in claim 3 which isN,N'-(1,4-tetramethylene)-bis[3,4,5,6-tetrabromophthalimide].